Most of the time if you're using a PDF reader like Acrobat or the like when you go into the print function it'll give you the opportunity to print actual size, as well as have check boxes for "choose paper source based on PDF size" and "use custom paper size when needed". It will then show you what the "native" size of the document is. I plot stuff on 36" wide plotters here at work on occasion.
word to the wise, if you print a PDF and it cuts off a piece of the plan, it's a quirk of the software, I've solved it by rotating the PDF 90 degrees and printing again. The Auto-portrait/landscape still prints it right, but rotating it seems to give the software a clue and you don't get an incomplete print.